JPH0581531B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing hexagonal plate-shaped substituted barium ferrite fine powder, and more particularly, to
The present invention relates to a method for producing spinel-type nickel ferrite modified hexagonal plate-like substituted barium ferrite powder having a temperature coefficient of 0.03 to 0.15 μm and a temperature coefficient of coercive force of +1 oersted/°C or less, which is in a small range including a negative region. Conventional technology The so-called hexagonal plate-shaped substituted barium ferrite fine powder represented by _{the general formula} BaO・n (Fe _12-2X Co Efforts are being made to utilize it as magnetic powder for density magnetic recording media. Various methods for producing such substituted barium ferrite fine powder are already known, and a wet method for producing the same is disclosed, for example, in JP-A-56-160328.
It is described in detail in Japanese Patent Application Laid-open No. 168532/1983. According to the latter publication, an alkaline aqueous solution containing barium ions, iron () ions, and substituted element ions with a pH of 12 or higher is heated to 150 to 300°C so as to satisfy the molar ratio of component elements in a predetermined substituted barium ferrite. by precipitating a barium ferrite precursor, and then calcining this precursor with a water-soluble barium halide, such as barium chloride, at a temperature of 700-1000°C, followed by removing the barium halide. , excellent hexagonal plate shape, and particle size of substantially 0.05~
It is stated that barium ferrite microcrystalline powder in the 0.5 μm range can be produced. BaO, a typical barium ferrite
6Fe ₂ O ₃ usually has a coercive force of 3000 to 6000 oersteds, but the above-mentioned substituted barium ferrites can generally be made suitable for magnetic recording by selecting the degree of substitution with Co and Ti. Ta
It can be made into a fine powder with a coercive force of 200 to 2000 oersteds. However, such conventional substituted barium ferrite fine powder has a tendency for coercive force to increase as the temperature rises. In other words, even if the magnetic field generated from the magnetic head is adjusted so that optimal recording is formed on the magnetic recording medium at room temperature, for example, if the environmental temperature rises, the coercive force increases and the magnetic field from the magnetic head increases. The generated magnetic field does not allow optimum recording to be formed on the magnetic recording medium. Furthermore, in conventional substitution type barium ferrite, erasability of magnetic recording often deteriorates depending on environmental conditions. In general, the temperature change in coercive force is calculated using the temperature coefficient formula C _{T C T = Hc 2 - Hc, where H C1 is the coercive force at temperature t 1 (°C) and H C2 is the coercive force at temperature t 2 ( ° C ) .} It is expressed as ₁ / _t2 - _t1 . However, temperatures t ₁ and t ₂ are both 100℃
The temperature is as follows, and t ₁ <t ₂ . Temperature coefficient of the above conventional substitution type barium ferrite fine powder
C _T is in the range +2 to +5 oersteds/°C. However, the preferred temperature coefficient range for magnetic recording materials is generally +1 to -2 oersted/°C. Therefore, in order to reduce the temperature dependence of the coercive force in such substitutional barium ferrite, for example, Japanese Patent Application Laid-Open No. 132732/1983 has proposed a method that is defined only by the maximum dimension of the plate-like surface/thickness of the grain. A method of increasing the axial ratio to 5 or more is described, and JP-A-61-152003 describes a method of incorporating Fe() ions. On the other hand, in order to improve the dispersibility of substituted barium ferrite, metal ions forming a spinel type oxide,
JP-A-62-265122 and JP-A-Sho disclose a method of coating a spinel-type ferrite on the surface by heating a slurry of barium ferrite containing Fe() ions and nitrate ions under highly alkaline conditions.
It is described in Publication No. 62-265123. Problems to be Solved by the Invention In order to solve the problems with the conventional substitutional type barium ferrite fine powder as a magnetic recording material, the present inventors have attempted to manufacture the above-mentioned conventional substitutional type barium ferrite fine powder and spinel. As a result of extensive research into methods involving the production of modified barium ferrite type nickel ferrite,
After preparing a substantially amorphous substituted barium ferrite precursor, adding a water-soluble nickel salt to the slurry and causing a hydrothermal reaction to produce spinel-type nickel ferrite on the surface of the precursor, By firing it with barium chloride, the temperature coefficient of coercive force increases by +1 Oersted/°C.
Below, a small range including the negative area, preferably +1
The present invention was achieved by discovering that it is possible to produce a spinel-type nickel ferrite modified substituted barium ferrite fine powder having a temperature in the range of -2 oersteds/°C. Means for Solving the Problems The method for producing plate-shaped barium fine powder according to the present invention includes (a) general formula BaO.n (Fe _12-2X Co _X Ti _X O ₁₈ ) (where n is a number from 0.8 to 1.0); and x is 0.5~
It is a number of 1.0. ) Ba ions and Fe ions were added to satisfy the molar ratio of component elements in barium ferrite expressed by
() Add an alkali to an aqueous solution containing ions, Co ions, and Ti ions to precipitate a coprecipitate, and heat it to 60°C or higher under normal pressure and alkalinity with a pH of 12 or higher to make it substantially non-stable. Co and
A first step of producing a Ti-substituted barium ferrite precursor, (b) Next, an aqueous Ni salt solution with a molar amount of 1 to 4 times the amount of Ba ions is added to the slurry of the barium ferrite precursor, and 150 to 300 a second step of producing a spinel-type nickel ferrite-modified barium ferrite precursor exhibiting a two-phase mixed phase of magnetoplumbite-type barium ferrite and spinel-type nickel ferrite through a hydrothermal reaction at a temperature of ℃; , a third step of sintering this spinel-type nickel ferrite modified barium ferrite precursor with barium chloride at a temperature of 800 to 950°C, and then eluting the barium chloride by washing with water, and by this method, Average particle size
0.03 to 0.15 μm and its temperature coefficient is +1
It is possible to obtain spinel-type nickel ferrite modified barium ferrite fine powder in a small range including a negative region of less than Oersted/°C. In the method of the present invention, first, as a first step, Ba ions, Fe() ions, Co An alkali is added to an aqueous solution containing ions and Ti ions to precipitate a coprecipitate, and under normal pressure,
This coprecipitate is heated and aged at 60°C or higher in an alkaline environment with a pH of 12 or higher to produce a substituted barium ferrite precursor. According to the method of the present invention, when preparing the alkaline aqueous solution containing the predetermined ions, it is necessary to set the molar ratio of the component ions to a predetermined range that satisfies the general formula, and n and x are If it is outside the specified range, please refer to the second and third
Even through these steps, it is difficult to obtain substituted barium ferrite microcrystalline powder with a small temperature coefficient. The method for preparing the alkaline aqueous solution is not limited in any way, but usually, aqueous solutions containing each of the above ions are prepared, and after mixing these at a predetermined temperature so as to contain each ion, this mixed aqueous solution is mixed. It is prepared by mixing it with an alkaline aqueous solution of a predetermined concentration. The aqueous solution containing each of the ions is prepared by dissolving each ion in a water-soluble compound,
Such water-soluble compounds are appropriately selected depending on the ion of each element, and usually non-acid salts or organic acid salts such as nitrates, perchlorates, chlorates, halides, sulfates, etc. are used. It will be done. Therefore, such water-soluble compounds include, for example, nitrates such as barium nitrate, ferric nitrate, cobalt nitrate, titanium nitrate, barium perchlorate, ferric perchlorate, cobalt perchlorate, perchlorate, etc. Perchlorates such as titanium chlorate, chlorates such as barium chloride, ferric chlorate, cobalt chlorate, chlorides such as barium chloride, ferric chloride, cobalt chloride, titanium tetrachloride. fluorides such as ferric fluoride, cobalt fluoride, and titanium fluoride; acetates such as barium acetate, ferric acetate, and gobalt acetate; and sulfates such as cobalt sulfate and titanium sulfate. be able to. When heating and ripening the coprecipitate, the alkaline aqueous solution must have a pH of 12 or higher. When the pH of the alkaline aqueous solution is lower than 12, the particle size remains at 0.15μ even after the second and third steps described below.
It is difficult to obtain substitution type plate-like barium ferrite powder with a particle size of less than m. In particular, the pH of the alkaline aqueous solution is preferably 13 or higher. As the alkali, a strong alkali is preferably used.
For example, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, etc. are used. These may be used alone or as a mixture of two or more. The heating temperature is preferably from 80°C to the boiling point under atmospheric pressure. The heating time is usually several tens of minutes to several hours. Chemically, the barium ferrite precursor obtained in this manner has a composition according to the above general formula, but crystals are hardly developed, and as a result of X-ray diffraction, it is an amorphous substance. Next, as a second step, an aqueous Ni salt solution is added to the slurry of the substituted barium ferrite precursor in a molar amount of 1 to 4 times the amount of Ba ions,
Subsequently, the barium ferrite precursor is heated at a temperature of 150 to 300° C. to an alkaline condition with a pH of 12 or more, preferably 13 or more, that is, a hydrothermal reaction is performed to generate spinel-type nickel ferrite on the surface of the barium ferrite precursor,
Obtain a spinel kelferrite modified barium precursor. In the method of the present invention, this second step is the most important. That is, by producing a barium ferrite precursor and then subjecting this precursor to a hydrothermal reaction in the presence of a water-soluble nickel salt, the temperature coefficient of coercive force can be increased by +1 oersted without substantially reducing saturation magnetization. /°C to a small range including the negative region. In the first step, Ni ions are allowed to coexist to obtain a coprecipitate, and when this is subjected to a hydrothermal reaction, the saturation magnetization decreases significantly, making barium ferrite fine powder suitable for use as a high-density magnetic recording material. can't get it. The nickel salt used in the second step is not particularly limited, and examples thereof include nickel nitrate, nickel perchlorate, nickel chlorate,
Inorganic salts such as nickel chloride and nickel nitrate are preferably used, but organic acid salts such as nickel acetate may also be used if necessary. When the amount of Ni salt used is less than 1 times the molar amount relative to the Ba ions, the temperature coefficient of the coercive force of the obtained barium ferrite is still large; It is not preferable to increase the temperature condition coefficient of coercivity because the absolute value of the coercive force increases in the negative direction and the saturation magnetization decreases. The hydrothermal reaction is usually carried out by heating the slurry of the barium ferrite precursor containing the Ni salt to a temperature in the range of 150 to 300°C using a closed container, such as an autoclave. The heating time is not limited, but is usually several tens of minutes to several hours. The spinel-type nickel ferrite-modified barium ferrite precursor obtained in the second step contains a small amount of amorphous material, but according to X-ray diffraction, it is a two-phase mixture of magnetoplumbite-type barium ferrite and spinel-type nickel ferrite. Show phase. However, this precursor has low saturation magnetization and cannot be used as a practical high-density magnetic recording material. Therefore, according to the method of the present invention, as the third step, the spinel-type nickel ferrite modified barium ferrite precursor obtained as described above is fired with barium chloride at a temperature of 800 to 950°C, and then washed with water. Therefore, the barium chloride is eluted and removed, and then dried and fired to complete the crystallization of the precursor into a hexagonal system, and to grow the precursor into a plate-like shape, thus resulting in spinel-type nickel ferrite modification. Substituted barium ferrite fine powder is obtained. That is, in the method of the present invention, by coexisting barium chloride when firing the spinel-type nickel ferrite modified barium ferrite precursor, crystal growth into a hexagonal plate shape is prevented while mutual fusion and sintering of particles is prevented. can be carried out completely and the particles can be sized.Thus, after firing, the fired product can be washed with water,
By eluting and removing the above-mentioned water-soluble barium chloride, it is possible to obtain spinel-type nickel ferrite modified barium ferrite fine powder having a particle size of 0.03 to 0.15 μm and excellent plate-like properties. The particle size herein refers to the maximum long axis of a hexagonal plate-like particle, that is, the maximum distance between opposing vertices. As described above, according to the method of the present invention, barium chloride is interposed between the precursor particles during firing, and this barium chloride acts as an anti-sintering agent and forms fine spinel-type nickel ferrite modified barium ferrite particles into hexagonal plate shapes. Since it acts as a particle size regulating agent for growth, the particles are separated from each other and diluted so to speak, so crystal growth into hexagonal plate shapes progresses without sintering between particles, and as a result, the particle shape becomes hexagonal. It is possible to obtain spinel-type nickel ferrite modified barium ferrite fine powder that is arranged in a plate shape, that is, has a high hexagonal plate shape. In the method of the present invention, the barium chloride is
50 parts by weight or more is used per 100 parts by weight of the spinel type nickel ferrite modified barium ferrite precursor. Since the amount of barium chloride used is too small and the diluting effect on the precursor is insufficient, particles are fused and sintered when the precursor is fired. On the other hand, this barium chloride is eluted from the fired product by washing the fired product with water after firing the precursor,
Since it is removed, it may be used in large excess with respect to the precursor, but even if it is used in particularly large excess, the elution and removal operation will take a long time and there is no particular advantage. In the method of the present invention, it is preferably used in a range of 100 to 200 parts by weight. In the method of the present invention, in order to sinter the spinel-type nickel ferrite-modified barium ferrite precursor to coexist with barium chloride, for example, the precursor is wet-kneaded with barium chloride, dried, and then After granulating or pulverizing as necessary, this may be fired at a predetermined temperature in an electric furnace. However, the method is not limited to this method. The firing temperature is preferably in the range of 800 to 900°C.
At temperatures lower than 800° C., the precursor is insufficiently crystallized, and the resulting spinel-type nickel ferrite modified barium powder has, for example, poorer magnetic properties, particularly low saturation magnetization. On the other hand, 950℃
When calcining at a high temperature exceeding Therefore, it is not particularly suitable for use as a magnetic recording material. In particular, according to the method of the present invention, the firing temperature is between 800 and 900.
A range of 0.degree. C. is preferred. Effects of the Invention As described above, according to the method of the present invention, a coprecipitate having a predetermined elemental ion composition is heated and aged,
Obtain a Co and Ti substituted barium ferrite precursor,
This is subjected to a hydrothermal reaction in the presence of nickel salt to produce spinel-type nickel ferrite on its surface, which is a spinel-type nickel ferrite-modified barium ferrite that exhibits a two-phase mixed phase of magnetopran type barium ferrite and spinel type nickel ferrite. A precursor is obtained, which is further fired to reduce the effects of the barium chloride sintering inhibitor and the particle size regulating agent. Therefore, according to the method of the present invention, the average particle size is substantially reduced.
In addition to being in the range of 0.03 to 0.15 μm, the temperature coefficient of coercive force is less than +1 Oe/°C, with a small negative region, usually in the range of +1 to -2 Oe/°C, and it is highly crystallized in a hexagonal plate shape. Substituted barium ferrite fine powder can be obtained. EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples in any way. Examples 1 to 5 3467 ml of ferric chloride aqueous solution with a concentration of 3 mol/
1000 ml of 1.0 mol/barium chloride aqueous solution, 800 ml of 1.0 mol/cobalt chloride aqueous solution and 1.0 mol/
After mixing 800 ml of titanium tetrachloride aqueous solution, this mixed aqueous solution was added to 7,600 ml of sodium hydroxide with a concentration of 15 mol/at a temperature of 15 to 20°C to precipitate a coprecipitate containing each of the above ions. An aqueous solution of was obtained. Next, the aqueous solution containing the coprecipitate was heated at 100°C for 4 hours with stirring to form BaO・n(Fe _10.4 Co _0.8
A slurry of a Co and Ti substituted barium ferrite precursor having a composition of Ti _0.8 O ₁₈ ) was obtained. Chemically, this precursor has a composition according to the above formula, but the crystals were not sufficiently developed, and it was confirmed from the X-ray diffraction image that it was amorphous. Next, various amounts of nickel chloride (NiCl ₂ ) aqueous solution were added to the slurry of the substituted barium ferrite precursor at a temperature of 100°C, and nickel hydroxide was deposited on the surface of the substituted barium ferrite precursor. The mixture was heated in an autoclave at 250° C. for 4 hours to obtain a spinel-type nickel ferrite modified barium ferrite precursor. This precursor was washed with water until the pH of the washing water became 8 or less, and then dried. The obtained spinel type nickel ferrite modified barium ferrite precursor contains a small amount of amorphous material, but according to X-ray diffraction, it is a two-phase mixed phase of magnetoplumbite type barium ferrite and spinel type nickel ferrite. It was confirmed that However, this precursor does not have sufficient magnetic properties, such as significantly low coercive force and saturation magnetization, and cannot be used as a practical high-density magnetic recording material. Next, 100 parts by weight of the spinel-type nickel ferrite modified barium ferrite precursor and 100 parts by weight of barium chloride were wet mixed with water, granulated into spherical particles having a particle size of about 3 mm, and then dried. After this, the dried precursor was heated in an electric furnace for 900 min.
After firing at ℃ for 3 hours, the fired product was coarsely ground,
Next, it was wet ground using a sand grinder. Next, this was washed with water to elute and remove barium chloride, filtered and dried to obtain a spinel type nickel ferrite modified barium ferrite fine powder according to the present invention. Using this vibrating sample magnetometer of barium ferrite powder, we measured the saturation magnetization (σ _S ) and coercive force (iHc).
and also based on the temperature change in coercive force,
The temperature coefficient was determined. The average particle size was measured from electron micrographs. The results are shown in Table 1. The fine Baium ferrite powder according to the present invention has a temperature coefficient of coercive force of +1 oersted/°C or less, which is in the small negative region. Comparative Examples 1 and 2 After preparing a slurry of substituted barium ferrite precursor in the same manner as in the above example, at a temperature of 100°C, the slurry was adjusted to 0.5 mol or 5.0 mol per 1 mol of Ba ions. , a nickel chloride aqueous solution was added thereto, and the same operations as in Examples were carried out to obtain spinel-type nickel ferrite modified barium ferrite fine powder. Regarding these, the magnetic properties and average particle size were
Shown in the table. The barium ferrite fine powder according to Comparative Example 1 has a temperature coefficient of coercive force of +2 oersted/
On the other hand, the barium ferato fine powder according to Comparative Example 2 has a negative temperature coefficient of coercive force and a large absolute value, and also has a low saturation magnetization of 30 emu/g.
Not practical. Comparative Example 3 Barium ferrite was prepared in exactly the same manner as in Example except that nickel chloride was not added. As shown in Table 1, the temperature coefficient of coercive force is +3.8 oersted/
It was warm at ℃. Comparative Example 4 2467 ml of ferric chloride aqueous solution with a concentration of 3 mol/
1000ml of 1.0mol/barium chloride aqueous solution, 800ml of 1.0mol/cobalt chloride aqueous solution, 1.0mol/
After mixing 800 ml of titanium tetrachloride aqueous solution and 1,500 ml of 1.0 mol/nickel chloride aqueous solution, this mixed aqueous solution was added to 7,600 ml of sodium hydroxide aqueous solution with a concentration of 15 mol/at a temperature of 15 to 20°C to remove each of the above ions. The coprecipitate containing the phthalate was precipitated to obtain an aqueous solution of PH14. Next, the aqueous solution containing the coprecipitate was heated at 100°C for 4 hours with stirring to form BaO・(Fe _1.4 Co _0.8
Co, Ni and Ti with the composition Ni _1.5 Ti _2.3 O ₁₈ )
Replacement type burr

[Table] A slurry of umferite precursor was obtained. Chemically, this precursor has a composition according to the above formula, but the crystals were not sufficiently developed, and it was confirmed from the X-ray diffraction image that it was amorphous. Next, the slurry of the barium ferrite precursor was heated in an autoclave at a temperature of 250°C for 4 hours.
By heating for a period of time, a Co, Ni and Ti substituted barium ferrite precursor was obtained. The pH of the water washing this precursor
After washing with water until the value became 8 or less, it was dried. The Co-, Ni-, and Ti-substituted barium ferrite precursor obtained here also contains a small amount of amorphous material, but according to X-ray diffraction, it consists only of a magnetoplumbite phase and no nickel ferrite phase exists. was confirmed. However, this precursor does not have sufficient magnetic properties, such as significantly low coercive force and saturation magnetization, and cannot be used as a practical high-density magnetic recording material. Next, the Co, Ni, and Ti substituted barium ferrite precursor was calcined with barium chloride at 900°C for 3 hours in the same manner as in Examples 1 to 5, and then the barium chloride was removed to form a Co, Ni, and Ti substituted barium ferrite precursor. Fine barium ferrite powder was obtained. The magnetic properties and average particle size of such barium ferrite fine powder are shown in Table 1, and the temperature coefficient of coercive force is -1.0.
Although the value of Oersted/°C is within the preferable range, the saturation magnetization is extremely low and cannot be put to practical use.

Claims (1)

[ _Claims ] 1 General formula _BaO ·n (Fe _{12-2X Co}
is the number of ) Add an alkali to an aqueous solution containing Ba ions, Fe() ions, Co ions, and Ti ions to precipitate a coprecipitate so as to satisfy the molar ratio of component elements in barium ferrite expressed by
Heating to 60℃ or higher in an alkaline environment with a pH of 12 or higher,
A first step of producing a substantially non-metallic Co- and Ti-substituted barium ferrite precursor, and then a molar amount of 1 to 4 times the amount of Ba ions.
An aqueous Ni salt solution is added to the slurry of the above barium ferrite precursor, and a hydrothermal reaction is performed at a temperature of 150 to 300°C to produce spinel-type nickel, which exhibits a two-phase mixed phase of magnetoplumbite-type barium ferrite and spinel-type nickel ferrite. a second step of producing a ferrite-modified barium ferrite precursor;
Next, this spinel-type nickel ferrite modified barium ferrite precursor was combined with barium chloride.
After firing at a temperature of 800 to 950°C, the barium chloride is eluted by washing with water. A method for producing spinel type nickel ferrite metamorphic substitution type barium ferrite fine powder having a temperature of /°C or less.